Semiconductor memory device having a plurality of chips and capability of outputting a busy signal

ABSTRACT

One package contains a plurality of memory chips. Each memory chip has an I/O terminal which generates a busy signal. The busy signal enables a busy state when a power supply voltage value reaches a specified and guaranteed range after a power-on sequence. The busy signal maintains the busy state until completion of initialization operations for the plurality of memory chips. The busy signal releases the busy state after completion of all initialization operations for the plurality of memory chips.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 11/904,565 filed Sep. 27, 2007(now U.S. Pat. No. 7,933,134 issued Apr. 26, 2011), which is a divisionof U.S. application Ser. No. 10/949,274, filed Sep. 24, 2004 now U.S.Pat. No. 7,542,323 issued Jun. 2, 2009, which is a continuation of U.S.application Ser. No. 10/754,993, filed Jan. 8, 2004 now U.S. Pat. No.6,990,003 issued Jan. 24, 2006, which is a continuation of U.S.application Ser. No. 10/185,645, filed Jun. 28, 2002 now U.S. Pat. No.6,680,858 issued Jan. 20, 2004, and claims the benefit of priority under35 U.S.C. §119 from Japanese Patent Application Nos. 2001-198132 filedJun. 29, 2001; No. 2001-377408 filed Dec. 11, 2001; and No. 2002-159518filed May 31, 2002, the entire contents of each of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor memory device such asan IC card, a memory system, etc. including a plurality of semiconductormemory chips in a package.

2. Description of the Related Art

As a semiconductor memory device, there is widely known an EEPROM(Electrically Erasable Programmable Read Only Memory) chip which enablesrewriting of data. With respect to large integration, particularattention is paid to a NAND-cell type EEPROM chip which configures aNAND cell by serially connecting a plurality of memory cells.

A memory device (chip) such as NAND-cell type EEPROM is generallyinitialized after a power-on sequence.

A memory chip such as NAND-cell type EEPROM comprises a large number ofintegrated memory cells. All memory cells are not fabricated normallyduring chip production. There is a high possibility of manufacturingdefective memory cells. If just a single defective memory cell isincluded, that chip is determined to be defective and must be discarded.However, this method greatly increases manufacturing costs of memorychips.

As a solution, for example, the NAND-cell type EEPROM provides a spareblock as a substitute for a defective memory cell. A block containingthe defective memory cell is replaced by the spare block in units ofblocks to normalize the memory chip containing the defective memory celland increase the non-defective rate.

As an example of the above-mentioned memory chip initialization, a spareblock is substituted for the block containing a defective memory cell.Another example is a voltage trimming operation for optimizing variousvoltages used inside a memory chip.

Normally, the initialization operation is set to a given period, e.g.,several hundreds of microseconds after the power supply voltage reachesa value within a specified range at the power-on time. During theinitialization period, the memory chip cannot be controlled from theoutside.

Conventionally, a system that uses the memory chip measures the time forthe initialization, determines the end of the initialization, and thencontrols the memory chip.

In this case, the system using the memory chip requires an extraoperation of measuring the time, complicating the memory chip control.

As a solution for this problem, the memory chip generates a busy signalat the power-on time. The busy signal indicates the busy state for aperiod after the power supply voltage reaches a value in the specifiedrange and until the memory chip becomes controllable from the outside.Regarding the busy state output, for example, the NAND-cell type EEPROMconventionally has a capability of outputting the memory chip's busystate during operations of reading, writing, or erasing data. There havebeen used a method of determining the busy state by (A) outputting thebusy state from a pad exclusively used for the busy state output or (B)outputting the busy state from an I/O pad immediately after a busy stateoutput command is entered, and then a data output enable state takeseffect.

Normally, systems or users use different methods of detecting the busystate. Convenience is improved by allowing the use of methods (A) and(B). Namely, both methods (A) and (B) are indispensable.

Conventionally, a package product mounted with a plurality of memorychips has been used for EEPROM, IC cards or memory systems containingmemory chips such as EEPROM. A widely used method allows one package toinclude a plurality of memory chips for increasing the memory capacityof an IC card, memory system, etc. One example is a package productincluding a plurality of nonvolatile memory chips.

On the package product including a plurality of memory chips, a busystate must be detected at the power-on time until the chipinitialization is complete for all nonvolatile memory chips in thepackage.

FIG. 1 is a block diagram schematically showing a conventional packagedmemory device including a plurality of memory chips. The example hereshows that two memory chips MC1 and MC2 are included. The memory chipsMC1 and MC2 in a memory device 10 are supplied with a power supplyvoltage Vcc and a ground voltage GND. Busy state output pads for thememory chips MC1 and MC2 are commonly connected to a busy state outputterminal 11. The output terminal 11 is connected to a node for the powersupply voltage Vcc via a load resistor 12. I/O pads of the memory chipsMC1 and MC2 are connected to an I/O terminal 13. The I/O terminal 13 isconnected to an I/O bus 14.

The output terminal 11 generates a busy signal /BusyA causing an “L”level when at least one of memory chips MC1 and MC2 is busy. A slash (/)for /BusyA indicates an inverted signal.

When a busy state output command is entered to the memory device 10, theI/O terminal 13 outputs busy signal /Busy1 or /Busy2. This busy signalcauses an “L” level when the corresponding memory chip is busy.

A package product containing a plurality of memory chips requires a busystate to be output until all memory chips in the package have beeninitialized after the power is turned on. Accordingly, busy states mustbe output from all the memory chips in the package. Each memory chipoutputs a signal representing the busy state via the I/O pad and the I/Oterminal 13.

Generally, an output time width for the busy signal at the power-on timedepends on chips and therefore differs among chips. When one chip isbusy, another may be ready, i.e., not busy.

FIG. 2 is a timing chart showing an example of operations after thepower is turned on until each chip becomes ready to be controlledexternally on the conventional memory device as shown in FIG. 1. Whenthe power is turned on and the power supply voltage exceeds a specifiedvalue, an initialization operation starts in each of the memory chipsMC1 and MC2. The period of this initialization is indicated with an “H”level. For example, let us assume that the memory chip MC2 requires alonger time for initialization than the memory chip MC1

After the initialization starts, the memory chips MC1 and MC2 outputbusy signals /Busy1 and /Busy2 indicative of the busy state via the I/Oterminal 13. The “L” levels of the busy signal /Busy1 and /Busy2correspond to the busy state. The busy state is released when theinitialization for each chip is complete. The busy signal /Busy2 becomesready after /Busy1. Namely, there is caused a different logical levelstate (TX in FIG. 2) between the busy signals /Busy1 and /Busy2. Duringthe TX period, the busy signal /Busy1 output from the memory chip MC1maintains the “H” level. The busy signal /Busy2 output from the memorychip MC2 maintains the “L” level. When the busy state output command isentered to the memory device 10 during the TX period, then busy signals/Busy1 and /Busy2 are output from the memory chips MC1 and MC2, a shortcircuit occurs between the power supply voltage Vcc and the groundvoltage GND via the memory chips MC1 and MC2. This short circuit maycause the chip to malfunction due to the raised ground voltage level orlowered supply voltage level in each chip. Each chip is generally set tocause a large amount of output current to flow from the I/O pad. A largeamount of current may flow between chips via the I/O bus 14, causing apossibility of destroying the device itself.

BRIEF SUMMARY OF THE INVENTION

An aspect of the present invention, there is provided a semiconductormemory device including a plurality of memory chips in a package,wherein a busy state takes effect when the power supply voltage reachesa specified value after a power-on sequence; the busy state ismaintained until completion of an initialization operation for theplurality of memory chips; and the busy state is released aftercompletion of all initialization operations for the plurality of memorychips.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram schematically showing a configuration of aconventional memory device;

FIG. 2 is a timing chart showing an example of operations in the memorydevice in FIG. 1;

FIG. 3 is a block diagram schematically showing a basic configuration ofa memory device according to the present invention;

FIG. 4 is a block diagram showing an internal configuration of thememory chip in FIG. 3;

FIG. 5A is a plan view of one NAND cell in the memory cell array in FIG.4 and FIG. 5B is an equivalent circuit diagram thereof;

FIGS. 6A and 6B are different sectional views of the NAND cell in FIGS.5A and 5B;

FIG. 7 is an equivalent circuit diagram of the memory cell array in FIG.4;

FIG. 8 is a circuit diagram specifically showing a partial configurationof a busy control circuit in a memory device according to a firstembodiment;

FIGS. 9A and 9B are circuit diagrams showing in detail a configurationof an output control circuit provided in the busy control circuit inFIG. 8;

FIGS. 10A and 10B are circuit diagrams showing in detail a configurationof the output control circuit provided in the busy control circuit inFIG. 8;

FIG. 11 is a timing chart showing an operation example of the busycontrol circuit using the output circuit in FIGS. 9A and 9B;

FIG. 12 is a timing chart showing an operation example of the busycontrol circuit using the output circuit in FIGS. 10A and 10B;

FIG. 13 is a circuit diagram specifically showing a partialconfiguration of a busy control circuit in a memory device according toa second embodiment;

FIG. 14 is a circuit diagram specifically showing a partialconfiguration of a busy control circuit in a memory device according toa third embodiment;

FIG. 15 is a circuit diagram specifically showing a partialconfiguration of a busy control circuit in a memory device according toa modification of the third embodiment;

FIG. 16 is a circuit diagram specifically showing a partialconfiguration of a busy control circuit in a memory device according toa fourth embodiment;

FIG. 17 is a circuit diagram specifically showing a partialconfiguration of a busy control circuit in a memory device according toa fifth embodiment;

FIG. 18 is a circuit diagram specifically showing a partialconfiguration of a busy control circuit in a memory device according toa sixth embodiment;

FIGS. 19A and 19B are circuit diagrams showing configurations of thecontrol circuits provided in the circuit according to the embodiment inFIG. 17;

FIG. 20 is a circuit diagram showing a configuration of another controlcircuit provided in the circuit according to the embodiment in FIG. 17;

FIG. 21 is a circuit diagram showing a detailed configuration of aswitch circuit in FIG. 20;

FIG. 22 is a circuit diagram showing another detailed configuration ofthe switch circuit in FIG. 20;

FIGS. 23A and 23B are circuit diagrams showing another configuration ofthe control circuits provided in the circuit according to the embodimentin FIG. 17;

FIG. 24 is a circuit diagram specifically showing a partialconfiguration of a busy control circuit in a memory device according toa seventh embodiment;

FIG. 25 is an equivalent circuit diagram showing another configurationof the memory cell array in FIG. 4;

FIG. 26 is an equivalent circuit diagram showing still anotherconfiguration of the memory cell array in FIG. 4;

FIG. 27 is an equivalent circuit diagram showing yet anotherconfiguration of the memory cell array in FIG. 4;

FIG. 28 is an equivalent circuit diagram showing still yet anotherconfiguration of the memory cell array in FIG. 4;

FIG. 29 is a circuit diagram showing a modified configuration of thecircuit embodied in FIG. 13;

FIG. 30 is a circuit diagram showing a modified configuration of thecircuit embodied in FIG. 14;

FIG. 31 is a circuit diagram showing a modified configuration of thecircuit embodied in FIG. 15;

FIG. 32 is a circuit diagram showing a modified configuration of thecircuit embodied in FIG. 16;

FIG. 33 is a circuit diagram showing a modified configuration of thecircuit embodied in FIG. 17;

FIGS. 34A and 34B are circuit diagrams showing another configuration ofthe control circuits provided in the circuit according to the embodimentin FIG. 17;

FIGS. 35A and 35B are circuit diagrams showing another configuration ofthe control circuits provided in the circuit according to the embodimentin FIG. 17;

FIG. 36 is a circuit diagrams showing another configuration of thecontrol circuits provided in the circuit according to the embodiment inFIG. 17; and

FIGS. 37A and 37B are circuit diagrams showing another configuration ofthe control circuits provided in the circuit according to the embodimentin FIG. 17.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in further detailwith reference to the accompanying drawings.

FIG. 3 is a block diagram schematically showing a basic configuration ofa memory device according to the present invention. The memory device 10contains a plurality of EEROM memory chips, each includes a plurality ofNAND cells, in a single package. In the example, there are included twomemory chips MC1 and MC2. It may be preferable to use two or more memorychips.

The memory chips MC1 and MC2 in the memory device 10 are supplied withthe power supply voltage Vcc and the ground voltage GND. Busy stateoutput pads for the memory chips MC1 and MC2 are commonly connected tothe busy state output terminal 11. The output terminal 11 is connectedto a node for the power supply voltage Vcc via the load resistor 12. I/Opads of the memory chips MC1 and MC2 are commonly connected inside thepackage and are further connected to the I/O terminal 13 of the memorydevice 10. The I/O terminal 13 is connected to an I/O bus 14.

The output terminal 11 generates a busy signal /BusyA causing an “L”level during a busy state of the memory chip MC1 or MC2, whichevercauses the longer busy state. A slash (/) for /BusyA signifies aninverted signal.

At least one wire 16 is provided between the memory chips MC1 and MC2.Each memory chip's busy state is transmitted therebetween via the wire16.

The I/O terminal 13 outputs busy signals /Busy1 and /Busy2.

A package product containing a plurality of memory chips requires a busystate to be output until all memory chips in the package have beeninitialized at the power-on time. Accordingly, busy states must beoutput from all the memory chips in the package. Each memory chipoutputs a signal representing the busy state via the I/O terminal 13.

The I/O terminal 13 outputs a busy state only in the data output enablestate. When a data output disable state takes effect, the I/O terminal13 always remains in a floating state. Accordingly, the busy signals/Busy1 and /Busy2 always go to the floating state in the data outputdisable state. Normally, a control pin (pad voltage in the chip) is usedfor control of the data output enable/disable states.

Basically, the following description about busy outputs of /Busy1 and/Busy2 refers to the above-mentioned method (B), i.e., states of /Busy1and /Busy2 in the data output enable state after a busy state outputcommand is entered.

FIG. 4 is a block diagram showing an internal configuration of each ofthe memory chips MC1 and MC2 in FIG. 3.

In FIG. 4, a memory cell array 21 is provided with a plurality ofNAND-type memory cells each having a control gate, a floating gate, anda select gate. The plurality of NAND cells are divided into blocks. Thememory cell array 21 connects with a bit line control circuit 22, a rowdecoder circuit 23, a well potential control circuit 24, a source linecontrol circuit 25, and a high/medium voltage generator circuit 26.

The bit line control circuit 22 connects with a column decoder circuit28 and a data input/output buffer 29. The column decoder circuit 25receives an address signal output from an address buffer 27. Accordingto an output signal from the column decoder circuit 28, the bit linecontrol circuit 22 reads, writes, rewrites, write-verifies,read-verifies, and erases data. Namely, the bit line control circuit 22mainly includes CMOS flip-flop circuits. The bit line control circuit 22latches data to be written into a memory cell, senses data for reading abit line potential or for a read-verify after writing, and latches datato be rewritten.

The row decoder circuit 23 connects with an address buffer 27, a wordline control circuit 30, and a row decoder power supply control circuit31. The row decoder circuit 23 controls the memory cell's control gateand select gate. The word line control circuit 30 controls a word linevoltage in a selected block. The row decoder power supply controlcircuit 31 controls the power supply voltage of the row decoder circuit23.

The well potential control circuit 24 controls a voltage of a p-typewell region or a p-type substrate where the memory cell array 21 isformed. The source line control circuit 25 controls a voltage of asource line in the memory cell array 21. The high/medium voltagegenerator circuit 26 generates a high voltage for erasing data and highand medium voltages for writing data. These voltages are supplied to thep-type well region being erased, to a word line being written via theword line control circuit 30, the row decoder power supply controlcircuit 31, and the row decoder circuit 23, and to a bit line via thebit line control circuit 22.

Each memory chip is further provided with a busy control circuit 32. Thebusy control circuit 32 outputs two types of busy signals /BusyA and/Busy1 (or /Busy2) indicative of the busy state. The busy signals areoutput at the power-on time after the power supply voltage reaches avalue in the specified and guaranteed range until the memory chipbecomes controllable from the outside. Alternatively, the busy signalsare output when data is read, written, or erased during normaloperations after the power-on sequence.

FIG. 5A is a plan view of one NAND-type memory cell in the memory cellarray 21 in FIG. 4. FIG. 5B is an equivalent circuit diagram of FIG. 5A.FIG. 6A is a cross-sectional view taken along lines 6A-6A in FIG. 5A.FIG. 6B is a cross-sectional view taken along lines 6B-6B in FIG. 5A.The same parts or components in FIGS. 5A, 5B, 6A, and 6B are depicted bythe same reference numerals.

As shown in FIGS. 5A, 5B, 6A, and 6B, a memory cell including aplurality of NAND cells which is formed in a p-type silicon substrate(or a p-type well region) surrounded by an element-isolation oxide film42. One NAND cell is provided with, e.g., eight memory cells M₁ throughM₈. The eight memory cells M₁ through M₈ are connected serially.

In each memory cell, there are formed floating gates 44 (44 ₁, 44 ₂, . .. , 44 ₈) on a substrate 41 via a gate insulating film 43. Above thefloating gates 44 (44 ₁, 44 ₂, . . . , 44 ₈), there are formed controlgates 46 (46 ₁, 46 ₂, . . . , 46 ₈) via a gate insulating film 45. Eachof n-type diffusion layers 49 ₁, 49 ₂, . . . , 49 ₈ configures a sourceand a drain of the memory cell. Adjacent n-type diffusion layers areshared to serially connect the memory cells.

The drain and source sides of each NAND cell are respectively providedwith the select gates 44 ₉ and 46 ₉, and 44 ₁₀ and 46 ₁₀. These selectgates are formed simultaneously with the memory cell's floating gate andcontrol gate. The substrate 41 where the memory cells are formed iscovered with an interlayer insulating film 47. A bit line 48 is formedon the interlayer insulating film 47. The bit line 48 is connected to adrain diffusion layer 49 ₀ at one end of the NAND cell.

The NAND cell's control gates 46 (46 ₁, 46 ₂, . . . , 46 ₈) are commonlyarranged in the row direction as control gate lines CG₁, CG₂, . . . ,and CG₈. These control gate lines are used as word lines. The selectgates 44 ₉ and 46 ₉, and 44 ₁₀ and 46 ₁₀ are also contiguously arrangedin the row direction and are used as select gate lines SG₁ and SG₂.

FIG. 7 shows an equivalent circuit of the memory cell array where theNAND cells are arranged in a matrix. A group of NAND cells shares theword line or the select gate line and is referred to as a block. An areaenclosed in a broken line in FIG. 7 is assumed to be one block.Normally, one of a plurality of blocks is selected for reading orwriting data in the memory cell.

The following describes operations of writing, erasing, and reading datain the above-mentioned NAND-cell type EEPROM.

A data write operation is performed sequentially from a memory cell atthe position farthest from the bit line contact. A high voltage Vpgm(e.g., approximately 18 V) is applied to the selected memory cell'scontrol gate. A medium voltage Vmw (e.g., approximately 10 V) is appliedto the memory cell's control gate and select gate. According to thedata, 0 V or a medium voltage Vmb (e.g., approximately 8 V) is appliedto the bit line.

When the bit line is supplied with 0 V, the potential is transmitted tothe selected memory cell's drain. A tunnel current causes electroninjection from the drain to the floating gate. At this time, theselected memory cell's threshold voltage shifts to positive value. Thisstate is assumed to be “1”, for example. When the bit line is suppliedwith the medium potential Vmb, no electron injection occurs.Accordingly, the threshold voltage does not change and remains to benegative. This state is assumed to be “0”.

Data is erased in units of blocks. Namely, data is erased at a time fromall memory cells in the selected NAND cell. In other words, all controlgates in the selected NAND cell block are set to 0 V. A high voltageVera (e.g., approximately 22 V) is applied to the p-type well region (orthe p-type substrate). A floating state is enabled for the bit line, thesource line, control gates in unselected NAND cell blocks, and allselect gate lines. Thus, the tunnel current emits a floating gate'selectron into the p-type well region (or the p-type substrate) andshifts the threshold voltage to the negative value in all memory cellsof the selected NAND cell block.

During a data read operation, the selected memory cell's control gate isset to 0 V. The control gates and the select gates of the other memorycells are approximately set to the power supply voltage Vcc or a readvoltage VH slightly higher than the power supply voltage. Normally, theread voltage VH is twice Vcc or less having a value of 5 V or less. Inthis state, data is sensed by detecting whether or not a current issupplied to the selected memory cell.

Let us assume that the memory device 10 in FIG. 3 provides control tokeep both the memory chips MC1 and MC2 busy until they are initializedcompletely. For this purpose, it is necessary to detect busy states ofthe other memory chips in the same package. To do this, there are twomethods: (1) detecting busy states of the other memory chips by usingthe busy signal /BusyA output from the busy state output terminal 11 and(2) detecting busy states of the other memory chips by using theexclusively used the wire 16 commonly connected to all chips in thepackage.

Method (1) has the advantage of preventing wires in the package or padsin the chip from increasing. However, the busy signal /BusyA is outputto the busy state output terminal 11 which is available outside the chipand may be subject to the wiring capacity, the voltage application, etc.in the system. Detailed examinations are needed with respect thereto.

According to method (2), the exclusively used wire is provided only inthe package and need not be provided outside the package, eliminatingthe need for detailed examinations with respect to the wiring capacity,the voltage application, etc. in the system. However, method (2) has adisadvantage of increasing the number of wires in the package or pads inthe chip. An examination should be made to select method (1) or (2)according to uses of the package product.

FIG. 8 is a circuit diagram specifically showing a partial configurationof the busy control circuit 32 in FIG. 4 which is provided in each ofthe two memory chips MC1 and MC2 in the memory device according to afirst embodiment of the present invention. In this case, theabove-mentioned method (2) is used.

The busy control circuit 32 has the same circuit configuration in bothmemory chips MC1 and MC2. The busy control circuits are represented bythe reference numerals 32-1 and 32-2 in the memory chips MC1 and MC2,respectively.

At the power-on time, the memory chips MC1 and MC2 generate internalbusy signals busy1 and busy2. Each of busy signals busy1 and busy2 issupplied to the gate of an N-channel MOS transistor 51 and one inputterminal of a 2-input NOR circuit 52 in the busy control circuits 32-1and 32-2. The source of the transistor 51 is connected to the groundvoltage node. The drain is connected to the busy state output terminal11 via the pad on the chip. As mentioned above, the terminal 11 isconnected to the node of the power supply voltage Vcc via the loadresistor 12.

The other input terminal of the 2-input NOR circuit 52 is mutuallysupplied with an internal busy signal generated in the other busycontrol circuit via one of two wires 16. The NOR circuit 52 forms adetection circuit for detecting busy states in the other memory chips.When a busy state output command is entered, each NOR circuit 52 outputsthe busy signals /Busy1 and /Busy2 to the corresponding I/O terminal 13via the I/O pad on the chip.

There is provided an output control circuit 53 between the output nodeof the NOR circuit 52 and the I/O terminal 13. The output controlcircuit 53 outputs a busy signal during a period after the power supplyvoltage reaches a value in the specified and guaranteed range at thepower-on time until the memory chip becomes controllable from theoutside. This period is referred to as a power-on reset period. Further,the output control circuit 53 outputs a busy signal in accordance with acommand input when data is read, written, or erased during normaloperations after termination of the power-on reset period.

FIGS. 9A and 9B and FIGS. 10A and 10B show in detail differentconfigurations of the output control circuit 53 provided in the circuitin FIG. 8.

The following details the output control circuit 53 shown in FIGS. 9Aand 9B and FIGS. 10A and 10B prior to description of operations of thecircuit in FIG. 8.

FIGS. 9A and 9B show detailed circuit configurations of the outputcontrol circuit 53 provided in the busy control circuits 32-1 and 32-2.Here, it is assumed that chip address 0 is assigned to the memory chipMC1 where the busy control circuit 32-1 is provided. Further, it isassumed that chip address 1 is assigned to the memory chip MC2 where thebusy control circuit 32-2 is provided.

As shown in FIG. 9A, the output control circuit 53 provided in the busycontrol circuit 32-1 includes a CMOS transfer gate 100, inverters 101and 102, NAND circuits 103 and 104, an AND circuit 105, and an inverter106. The CMOS transfer gate 100 provides the parallel source/drainconnection in P-channel and N-channel MOS transistors.

The inverters 101 and 102 each invert a power-on reset signal POR whichgoes to the “H” level during a power-on reset period. The NAND circuit103 is supplied with an output from the inverter 102 and a chip selectsignal chip select0 which goes to the “H” level in response to selectionof the memory chip MC1 provided with the busy control circuit 32-1. TheNAND circuit 104 is supplied with outputs from the inverter 101 and theNAND circuit 103. The AND circuit 105 is supplied with an output fromthe NAND circuit 104 and a Busy-Status-Output signal. The inverter 106inverts an output from the AND circuit 105. Outputs from the AND circuit105 and the inverter 106 are supplied to the N-channel and P-channel MOStransistors' gates in the CMOS transfer gate 100. After the busy stateoutput command is entered, and then the data output enable state takeseffect, the Busy-Status-Output signal becomes “H” level. Accordingly,when the Busy-Status-Output signal is “H” level, the busy signals /Busy1and /Busy2 are output to the I/O terminal 13.

FIG. 9B shows the output control circuit 53 provided in the busy controlcircuit 32-2. This busy control circuit has basically the sameconfiguration as for the circuit in FIG. 9A. A difference from FIG. 9Ais that the NAND circuit 103 is supplied with the chip select signalchip select1 instead of chip select0. The chip select signal chipselect1 goes to the “H” level in response to selection of the memorychip MC2 provided with the busy control circuit 32-2.

During the power-on reset period, the power-on reset signal POR goes tothe “H” level. At this time, an output from the inverter 101 goes to the“L” level. An output from the NAND circuit 104 goes to the “H” level.Accordingly, each CMOS transfer gate 100 goes on in the busy controlcircuits 32-1 and 32-2. The busy signals /Busy1 and /Busy2 output fromthe NOR circuit 52 in FIG. 8 are passed to each output control circuit53 and are output to the I/O terminal 13 via the I/O pad on each chip.

When using the output control circuit 53 according to the configurationsas shown in FIGS. 9A and 9B, all memory chips in the memory device 10output a busy signal from the I/O terminal during the power-on resetperiod.

Not all memory chips in the memory device 10 need to be used to outputthe busy signal from the I/O terminal. For doing this, it is alsopossible to use a single chip in the memory device, e.g., the chip withchip address 0. Also when a single chip is used, the chip for outputuses a signal on the wire 16 to detect the busy state of the other chipsand outputs the busy state reflecting this detection result.Consequently, the memory device 10 can correctly output the busy state.FIGS. 10A and 10B show circuit configuration examples for implementing amethod of outputting the busy state by using a single chip with chipaddress 0.

FIGS. 10A and 10B show detailed circuit configurations of the outputcontrol circuit 53. Here, it is assumed that chip address 0 is assignedto the memory chip MC1 where the busy control circuit 32-1 is provided.Further, it is assumed that chip address 1 is assigned to the memorychip MC2 where the busy control circuit 32-2 is provided.

As shown in FIG. 10A, the output control circuit 53 provided in the busycontrol circuit 32-1 includes a CMOS transfer gate 100, a NAND circuit107, an inverter 102, a NAND circuit 103, a NAND circuit 104, an ANDcircuit 105, and an inverter 106. The CMOS transfer gate 100 providesthe parallel source/drain connection in P-channel and N-channel MOStransistors. The NAND circuit 107 is supplied with a power-on resetsignal POR going to the “H” level during the power-on reset period and asignal chip Add0 going to the “H” level only in the chip with chipaddress 0 (going to the “L” level in chips in the other chip addresses).The inverter 102 inverts the reset signal POR. The NAND circuit 103 issupplied with an output from the inverter 102 and a chip select signalchip select0 going to the “H” level in response to selection of thememory chip MC1 provided with the busy control circuit 32-1. The NANDcircuit 104 is supplied with outputs from the both NAND circuits 107 and103. The AND circuit 105 is supplied with output from the NAND circuit104 and the Busy-Status-Signal. The inverter 106 inverts the output fromthe AND circuit 105. Outputs from the AND circuit 105 and the inverter106 are supplied to the N-channel and P-channel MOS transistors' gatesin the CMOS transfer gate 100.

FIG. 10B shows the output control circuit 53 provided in the busycontrol circuit 32-2. This busy control circuit has basically the sameconfiguration as for the circuit in FIG. 10A. A difference from FIG. 10Ais that the NAND circuit 103 is supplied with the chip select signalchip select1 instead of chip select0. As shown in FIG. 10B, the NANDcircuit 107 is supplied with chip Add0 as a chip address similarly toFIG. 10A. The chip address signal chip Add0 goes to the “H” level in thememory chip MC1, i.e., in the busy control circuit 32-1. The chipaddress signal chip Add0 goes to the “L” level in the memory chip MC2,i.e., in the busy control circuit 32-2. During the power-on resetperiod, a busy signal is output to the I/O terminal 13 from only thememory chip MC1.

After completion of the power-on reset period, the same operation isperformed whether the output control circuit in FIGS. 9A and 9B or FIGS.10A and 10B is used. After completion of the power-on reset period, anoutput from the inverter 102 goes to the “H” level. When a busy signalis output in response to command input during operations of reading,writing, and erasing data, only the selected chip's chip select signalgoes to the “H” level. When a chip select signal with the selectionstate enabled is input to the NAND circuit 103, an output from thiscircuit goes to the “L” level. When the memory chip is selected, anoutput from the NAND circuit 104 in the memory chip goes to the “H”level. After the busy state output command is entered, and then the dataoutput enable state takes effect, this state turns on only the CMOStransfer gate 100 in the busy control circuit of the selected memorychip. The busy signal /Busy1 or /Busy2 output from the NOR circuit 52 ispassed to the output control circuit 53, and then is output to the I/Oterminal 13 via the I/O pad on the chip.

Referring now to timing charts in FIGS. 11 and 12, the followingdescribes an example of operations in the memory device in FIG. 8according to the first embodiment after the power is turned on until twomemory chips MC1 and MC2 become controllable from the outside. In FIGS.11 and 12, the /Busy1 and /Busy2 levels are used to show output levelsof data from the I/O terminal 13 when the data output from the I/Oterminal is enabled. When the data output is disabled, the I/O terminal13 always becomes the floating state. This state corresponds to thepower-on reset period. When the circuits in FIGS. 9A and 9B are used asthe output control circuits 53, and the data output enable state takeseffect, the /Busy1 and /Busy2 signals are output from the both outputcontrol circuits 53 in the busy control circuits 32-1 and 32-2(equivalent to FIG. 11). When the circuits in FIGS. 10A and 10B are usedas the output control circuits 53, the /Busy1 and /Busy2 signals areoutput from only the output control circuit 53 in the busy controlcircuit 32-1 (equivalent to FIG. 12).

When the power is turned on and the power supply voltage exceeds aspecified value, an initialization operation starts in each of thememory chips MC1 and MC2. The period for this initialization isindicated by the “H” level. The internal busy signals busy1 and busy2maintain the “H” level during the initialization operation. Here, it isassumed that the memory chip MC2 requires a longer time for theinitialization than the memory chip MC1.

When the initialization is complete for the memory chip MC1, theinternal busy signal busy1 changes from the “H” level to the “L” level.In this case, however, the initialization is still in process for theother memory chip MC2. The internal busy signal busy2 remains at the “H”level. Accordingly, the busy signal /Busy1 remains at the “L” level. Thebusy signal /Busy1 is an output from the NOR circuit 52 in the busycontrol circuit 32-1 for the memory chip MC1. When the initialization iscomplete for the memory chip MC2, the internal busy signal busy2 changesfrom the “H” level to the “L” level. At this time, the busy signal/Busy1 for the memory chip MC1 changes to the “H” level.

When the initialization is complete for the memory chip MC2 according toFIG. 11 (using the circuits in FIGS. 9A and 9B), the internal busysignal busy2 changes from the “H” level to the “L” level. At this time,the busy signal /Busy2 changes to the “H” level. Namely, the busysignals /Busy1 and /Busy2 have the same busy period (“L” level).According to FIG. 12 (using the circuits in FIGS. 10A and 10B), thememory chip MC2 maintains the floating state for the output node (thenode for the busy signal /Busy2) during the initialization period.

The transistor 51 turns on during the “H” level period for the internalbusy signals busy1 and busy2 in the memory chips MC1 and MC2. The busystate output terminal 11 goes to the “L” level. The busy signal /BusyAoutput from the busy state output terminal 11 is set to the “L” levelduring a busy period corresponding to the internal busy signal busy1 orbusy2 whichever causes the longer busy period. This is effective whetherthe circuits in FIGS. 9A and 9B or FIGS. 10A and 10B are used. Namely,the signal waveform of the busy signal /BusyA becomes practically thesame as that of the /Busy1 or /Busy2.

A memory device having the busy control circuit as shown in FIG. 8eliminates a period in which the busy signals /Busy1 and /Busy2 are setto different logical levels from each other. This prevents a shortcircuit between the power supply voltage Vcc and the ground voltage GNDvia the memory chips MC1 and MC2. Consequently, it is possible to solveall the above-mentioned various problems due to existence of a period inwhich the busy signals /Busy1 and /Busy2 are set to different logicallevels from each other.

FIG. 13 is a circuit diagram specifically showing a partialconfiguration of the busy control circuit 32 in the memory deviceaccording to a second embodiment of the present invention. In this case,the above-mentioned method (1) is used.

The busy control circuit 32 has the same circuit configuration in bothmemory chips MC1 and MC2. The busy control circuits are represented bythe reference numerals 32-1 and 32-2 in the memory chips MC1 and MC2,respectively. The busy control circuits 32-1 and 32-2 each are providedwith the N-channel MOS transistor 51, the output control circuit 53, andthe 2-input AND circuit 54. The gate of the MOS transistor 51 issupplied with internal busy signals busy1 and busy2 generated in thememory chips MC1 and MC2. The source of the transistor 51 is connectedto the ground voltage node. The drain is connected to the busy stateoutput terminal 11 via the busy state output pad on the chip. Theterminal 11 is connected to the node of the power supply voltage Vcc viathe load resistor 12.

The input terminal of the AND circuit 54 is supplied with an invertedsignal /busy1 (/busy2) of the internal busy signal busy1 (busy2) and thebusy signal /BusyA output from the busy state output terminal 11. Anoutput from the AND circuit 54 is fed to the I/O terminal 13 via theoutput control circuit 53.

In this case, the AND circuit 54 is configured to be a detection circuitfor detecting busy states of the other memory chips. When a busy stateoutput command is entered to enable the data output, each AND circuit 54outputs the busy signal /Busy1 or /Busy2 to the I/O terminal 13.

In the memory device in FIG. 13 according to the second embodiment, anoutput signal from the AND circuit 53 goes to the “L” level when eitherof the two input signals stays at the “L” level. The “L” level periodfor the busy signals /Busy1 and /Busy2 is determined by the internalbusy signal busy1 or busy2 or the busy signal /BusyA whichever causesthe longer “L” level period.

Accordingly, the memory device also eliminates a period in which thebusy signals /Busy1 and /Busy2 are set to different logical levels fromeach other. This prevents a short circuit between the power supplyvoltage Vcc and the ground voltage GND between the memory chips MC1 andMC2 via the I/O bus 14 (see FIG. 3). Also in the case of FIG. 13, signalwaveforms of the busy signals /Busy1 and /Busy2 are the same as those inFIGS. 10A, 10B and 12

FIG. 14 is a circuit diagram specifically showing a partialconfiguration of the busy control circuit 32 in the memory deviceaccording to a third embodiment of the present invention. In this case,the above-mentioned method (2) is used.

The busy control circuit 32 has the same circuit configuration in bothmemory chips MC1 and MC2. The busy control circuits are represented bythe reference numerals 32-1 and 32-2 in the memory chips MC1 and MC2,respectively.

The busy control circuits 32-1 and 32-2 each are provided with theN-channel MOS transistor 51, the output control circuit 53, the 2-inputAND circuit 55, an N-channel MOS transistor 56, and a load resistor 57.The gate of the MOS transistor 51 is supplied with internal busy signalsbusy1 and busy2 generated in the memory chips MC1 and MC2. The source ofthe transistor 51 is connected to the ground voltage node. The drain isconnected to the busy state output terminal 11 via the busy state outputpad on the chip. The terminal 11 is connected to the node of the powersupply voltage Vcc via the load resistor 12.

One input terminal of the AND circuit 55 is supplied with an invertedsignal /busy1 (/busy2) of the internal busy signal busy1 (busy2). Thesource/drain region of the MOS transistor 56 are inserted between theother input terminal of the AND circuit 55 and the ground voltage node.The MOS transistor 56 functions as a switch. The internal busy signalbusy1 is input to the gate of the MOS transistor 56. The load resistor57 is connected between the other input terminal of the AND circuit 55and the node of the power supply voltage Vcc. The drain of the MOStransistor 56, i.e., the other input terminal of the AND circuit 55 iscommonly connected between different chips via the wire 16. An outputfrom the AND circuit 55 is fed to the I/O terminal 13 via the outputcontrol circuit 53.

In this case, a circuit including the AND circuit 55, the MOS transistor56, and the load resistor 57 is configured to be a detection circuit fordetecting busy states of the other memory chips. When a busy stateoutput command is entered to enable the data output, each AND circuit 55outputs the busy signal /Busy1 or /Busy2 from the I/O terminal 13 viathe output control circuit 53 and the I/O pad on the chip.

In the memory device in FIG. 14 according to the third embodiment, theMOS transistor 56 is controlled by the internal busy signals busy1 andbusy2. The wire 16 is used to commonly connect the drain of the MOStransistor 56, i.e., the other input terminal of the AND circuit 55between different chips. An input signal to the other input terminal ofthe AND circuit 55 is set to the “L” level by the internal busy signalbusy1 or busy2 whichever causes the longer “H” level period while thatsignal maintains the “H” level.

After the power is turned on, an output signal from the AND circuit 55goes to the “H” level when two input signals concurrently go to the “H”level. Also in this case, the memory device eliminates a period in whichthe busy signals /Busy1 and /Busy2 are set to different logical levelsfrom each other. This prevents a short circuit between the power supplyvoltage Vcc and the ground voltage GND between the memory chips MC1 andMC2 via the I/O terminal 13 (see FIG. 3).

FIG. 15 shows a memory device according to a modification of the thirdembodiment. The busy control circuits 32-1 and 32-2 in the memory deviceaccording to the modification have basically the same configuration asthat shown in FIG. 14. The mutually corresponding parts in FIGS. 15 and14 are designated by the same reference numerals and a detaileddescription is omitted for simplicity. The following describes onlyportions that differ from FIG. 14.

The MOS transistor 51 in FIG. 14 is omitted from the busy controlcircuits 32-1 and 32-2 in the memory device according to themodification. The load resistor 12 is connected to the common drain ofthe MOS transistor 56, i.e., to the wire 17. This is because the busystate output terminal 11 is also used with the wire in FIG. 14.

The memory device in FIG. 15 according to the modification of the thirdembodiment provides the same effects as those described with referenceto FIG. 14. Because the transistor 51 is not used, there is anadditional advantage of decreasing the number of elements compared toFIG. 14.

As described in the first through third embodiments and themodification, the load resistor 12 is connected outside the chip to thebusy state output terminal 11 or the wire 17 where the busy signal/BusyA is output. The terminal 11 or the wire 17 is always pulled up tothe “H” level (Vcc).

However, the present invention is also applicable when the busy stateoutput terminal 11 is not always pulled up to the “H” level outside thechip.

Generally, two methods of detecting the busy state of a package productare available: (A) always pulling up the busy state output terminal tothe “H” level for detecting a signal at this terminal and (B) outputtinga signal from the I/O pad after entering a busy state output command toenable the data output. When using only method (B), a user or a systemdoes not detect the busy state by using the busy state output terminal11. It is unnecessary to pull up the busy state output terminal 11 tothe “H” level outside the chip.

FIG. 16 shows a memory device according to a fourth embodiment of thepresent invention by using the above-mentioned method (B). FIG. 16 is acircuit diagram specifically showing a partial configuration of the busycontrol circuit 32 in FIG. 4 provided for each of the two memory chipsMC1 and MC2 in FIG. 3.

The busy control circuit 32 has the same circuit configuration in bothmemory chips MC1 and MC2. The busy control circuits are represented bythe reference numerals 32-1 and 32-2 in the memory chips MC1 and MC2,respectively. The busy control circuits 32-1 and 32-2 in the memorydevice according to the fourth embodiment have basically the sameconfiguration as that shown in FIG. 15. The mutually corresponding partsin FIGS. 16 and 15 are designated by the same reference numerals and adetailed description is omitted for simplicity. The following describesonly portions that differ from FIG. 15.

As mentioned above, the user or the system does not monitor the wire forbusy state output in the memory device according to the fourthembodiment. Accordingly, there is not provided the load resistor 12connected to the wire 17. The wire 17 mutually connects the memory chipsMC1 and MC2 with each other. The busy signal /BusyA is output from eachof the memory chips MC1 and MC2 to the busy state output pad. Basically,the pad is not connected outside the chip.

The busy state output pads in both chips are commonly connected to thewire 17. In order to detect a signal on the wire 17 for busy statedetection, the node of the wire 17 needs to be pulled up to the “H”level. The load resistor 57 is provided in each of the busy controlcircuits 32-1 and 32-2, and is used as an element for pulling up thenode of e wire 17.

Also in the memory device according to the embodiment, a busy signal isinterchanged between different busy control circuits via the wire 17.The memory device eliminates a period in which the busy signals /Busy1and /Busy2 are set to different logical levels from each other. Thisprevents a short circuit between the power supply voltage Vcc and theground voltage GND between the memory chips MC1 and MC2 via the I/Oterminal 13 (see FIG. 3).

FIG. 17 shows a memory device according to a fifth embodiment of thepresent invention by using the above-mentioned method (B) when the useror the system does not monitor the wire 17 for busy state output. FIG.17 is a circuit diagram specifically showing a partial configuration ofthe busy control circuit 32 in FIG. 4 provided for each of the twomemory chips MC1 and MC2 in FIG. 3.

The busy control circuit 32 has the same circuit configuration in bothmemory chips MC1 and MC2. The busy control circuits are represented bythe reference numerals 32-1 and 32-2 in the memory chips MC1 and MC2,respectively. The busy control circuits 32-1 and 32-2 in the memorydevice according to the fifth embodiment have basically the sameconfiguration as that shown in FIG. 16. The mutually corresponding partsin FIGS. 17 and 16 are designated by the same reference numerals and adetailed description is omitted for simplicity. The following describesonly portions that differ from FIG. 16.

The memory device according to the embodiment differs from that in FIG.16 as follows. The source/drain region of a P-channel MOS transistor 58is inserted between the load resistor 57 and the node of the powersupply voltage Vcc in the busy control circuits 32-1 and 32-2. A controlsignal P1 or P2 is used to control the gate of the MOS transistor 58.

In this configuration, the P-channel MOS transistor 58 is controlled bythe control signal P1 or P2 to on-state during the period after the chipinitialization starts at the power-on time until all memory chips havebeen initialized. The node of the wire 17 is pulled up to the “H” levelonly while the package product is initialized. After the initializationis complete, the MOS transistor 58 is turned off, saving an electriccurrent.

In the busy state, each of the memory chips MC1 and MC2 enables the “L”level for the I/O pad which outputs the busy signal /Busy1 or /Busy2.Sizes and so on of the MOS transistors 58 and 56 are predetermined sothat the current drive force of the N-channel MOS transistor 56 becomeshigher than that of the P-channel MOS transistor 58 and the loadresistor 57.

The memory device according to the embodiment provides the same effectsas those of the first through fourth embodiments and the modificationthereof. Further, there is an additional advantage of saving an electriccurrent after completion of the initialization operation.

When only one memory chip is provided in the package, it is unnecessaryto detect busy states of the other memory chips, eliminating the needfor the function of pulling up the node of the busy signal /BusyA. Inthis case, it is effective to disable exactly the operation of pullingup the node of the busy signal /BusyA.

FIG. 18 shows a memory device according to a sixth embodiment of thepresent invention by using the above-mentioned method (B) when the useror the system does not monitor the busy state output terminal 11. FIG.18 is a circuit diagram specifically showing a partial configuration ofthe busy control circuit 32 in FIG. 4 when there is provided either ofthe two memory chips MC1 and MC2 in FIG. 3.

The busy control circuits 32-1 and 32-2 in the memory device accordingto the sixth embodiment have basically the same configuration as thatshown in FIG. 17. The mutually corresponding parts in FIGS. 18 and 17are designated by the same reference numerals and a detailed descriptionis omitted for simplicity.

The memory device according to the embodiment is provided with only onememory chip. The “H” level always takes effect for the control signal P1input to the gate of the P-channel MOS transistor 58. The MOS transistor58 always remains off.

When the memory device is provided with a plurality of memory chips asshown in FIG. 17, nodes for the busy signal /BusyA can be simultaneouslypulled up for all memory chips in the memory device during theinitialization at the power-on time. In this case, it is unnecessary todistinguish memory chips in the memory device, providing an advantage ofsimplified control. However, all memory chips on the memory deviceconsume an electric current, increasing the power consumption.

As a solution, control may be provided to pull up nodes for the busysignal /BusyA only in some memory chips on the memory device. Thisdecreases the consumed current and highly effectively improves the powerconsumption.

There are available the following methods of controlling which memorychips in the memory device should pull up nodes for the busy signal/BusyA.

Normally, when the package is provided with a plurality of memory chips,different chip addresses are allocated to the chips for selecting themdistinctively. There is a method of pulling up the node for the busysignal /BusyA only in a chip having the smallest allocated chip address(e.g., the chip having the address 0). Another method is to pull up thenode for the busy signal /BusyA only in chips having even-numbered (orodd-numbered) chip addresses.

When the package is provided with a plurality of memory chips, it isvery effective with respect to power consumption to pull up nodes forthe busy signal /BusyA in some memory chips. This method prevents nodesfor the busy signal /BusyA from being pulled up simultaneously in allmemory chips. Implementation of this method requires an additionalcontrol circuit for setting logical levels of the control signals P1 andP2 based on the chip addresses so as to control the on/off state of theMOS transistor 58 according to the chip addresses.

FIGS. 19A and 19B show configurations of the control circuits foractivating only the P-channel MOS transistor 58 in a chip with thesmallest chip address, i.e., in the busy control circuit 32-1 accordingto the embodiment in FIG. 17.

The control circuit in FIG. 19A is provided in the busy control circuit32-1. The control circuit includes an inverter 111 and a NAND circuit112. The inverter 111 inverts the control signal P1. The NAND circuit112 is supplied with an output from the inverter 111 and a chip addresschip Add0. An output from the NAND circuit 112 is supplied to the gateof the P-channel MOS transistor (PMOS) 58 in the busy control circuit32-1.

The control circuit in FIG. 19B has basically the same configuration asthat in FIG. 19A. The only difference is that the control signal P2 isinput to the inverter 111 in FIG. 19B. An output from the NAND circuit112 is supplied to the gate of the P-channel MOS transistor (PMOS) 58 inthe busy control circuit 32-2.

Here, it is assumed that chip address chip Add0 is allocated to thememory chip MC1 where the busy control circuit 32-1 is provided and thatchip address chip Add1 is allocated to the memory chip MC2 where thebusy control circuit 32-2 is provided. Then, the chip address chip Add0supplied to the busy control circuit 32-1 is the “H” level. The chipaddress chip Add0 supplied to the busy control circuit 32-2 is the “L”level. When the control signal P1 maintains the “L” level, an outputfrom the NAND circuit 112 on the busy control circuit 32-1 goes to the“L” level, activating the P-channel MOS transistor 58 on the busycontrol circuit 32-1. Namely, the MOS transistor 58 is activated only inthe memory chip MC1 to pull up the node for the busy signal /BusyA.

The memory device in FIG. 17 according to the fifth embodiment controlsthe on/off state of the MOS transistor 58 based on the number of memorychips installed and chip addresses. Thus, the power consumption can bedecreased.

Normally, when a plurality of memory chips is mounted on a packageproduct, the chip addresses therein can be specified as follows. Onemethod is to select a bonding option to supply a specified potential toa specified pad by means of bonding. Another method is to selectivelyblow fuses in the chip.

FIG. 20 shows a configuration of another control circuit to activate theP-channel MOS transistor 58 in only one chip based on a chip addressaccording to the embodiment in FIG. 17.

FIG. 20 shows a partial configuration of the busy control circuit 32-1in the memory chip MC1, for example. The chip address chip Add0corresponds to the memory chip MC1 and is supplied to one input terminalof the NOR circuit 114 via a switch circuit 113. The chip address chipAdd1 corresponds to the memory chip MC2 and is supplied to the otherinput terminal of the NOR circuit 114 via a switch circuit 115. Anoutput from the NOR circuit 114 is supplied to one input terminal of aNAND circuit 117 via an inverter 116. The other input terminal of theNAND circuit 117 is supplied with the control signal P1 via an inverter118.

It is assumed that one of switch circuits 113 and 115 is controlled toturn on in this configuration. For example, the switch circuit 113 isassumed to turn on. When the chip address chip Add0 is input, it issupplied to the NOR circuit 114 via the switch circuit 113. An outputfrom the NOR circuit 114 becomes the “L” level. At this time, an outputfrom the inverter 116 becomes the “H” level. When the control signal P1maintains the “L” level, an output from the NAND circuit 117 becomes the“L” level, activating the P-channel MOS transistor in the busy controlcircuit 32-1 in FIG. 17.

When the switch circuit 115 is also controlled to turn on, both the chipaddresses chip Add0 and chip Add1 are input to the NOR circuit 114 viathe switch circuits 113 and 115.

FIG. 21 shows a detailed configuration of the switch circuit 113 or 115in FIG. 20. The switch circuit controls chip address output by means ofa bonding option. The switch circuit includes a CMOS transfer gate 200,a resistor 201, a pad 202, an inverter 203, and an N-channel MOStransistor 204. The CMOS transfer gate 200 provides parallel connectionbetween source/drain regions of the P-channel and N-channel MOStransistors. The pad 202 is pulled up to Vcc via the resistor 201. Aninput terminal of the inverter 203 is connected to the pad 202. In theN-channel MOS transistor 204, the source/drain region is connectedbetween the output node of the CMOS transfer gate 200 and the groundvoltage node. The gate is supplied with an output from the inverter 203.A signal from the pad 202 and an output from the inverter 203 aresupplied to the gates of the N-channel and the P-channel MOS transistorof the CMOS transfer gate 200.

In this configuration, when the pad 202 is not connected to the groundvoltage node by using a bonding wire, the pad 202 is pulled up to the“H” level via the resistor 201. Then, the CMOS transfer gate 200 turnson. When the CMOS transfer gate 200 turns on, the chip address chip Add0or chip Add1 is input to the NOR circuit 114 via the CMOS transfer gate200.

When a bonding wire 205 is used to connect the pad 202 to the groundvoltage node as shown in FIG. 21, the pad 202 becomes the “L” level. TheCMOS transfer gate 200 turns off. At this time, an output from theinverter 203 becomes the “H” level. The N-channel MOS transistor 204turns on. The output node for the CMOS transfer gate 200 is set to theground voltage.

The circuit in FIG. 21 can use the bonding wire 205 to connect or not toconnect the pad 202 to the ground voltage node for selectivelycontrolling chip address output.

FIG. 22 shows another detailed configuration of the switch circuit 113or 115 in FIG. 20. The switch circuit controls chip address output byselectively blowing fuses on the chip. The configuration of the switchcircuit partly differs from that of the switch circuit in FIG. 21. Adescription is omitted for the same portions as in FIG. 21. Thefollowing describes only portions that differ from FIG. 21.

In this switch circuit, a fuse 206 is connected between the input nodeof the inverter 203 and the ground voltage node. The fuse 206 can beblown by electromagnetic irradiation, for example.

When the fuse 206 is blown in this configuration, the pad 202 is pulledup to the “H” level via the resistor 201, turning on the CMOS transfergate 200. When the CMOS transfer gate 200 keeps the ON state, the chipaddress chip Add0 or chip Add1 is input to the NOR circuit 114 via theCMOS transfer gate 200.

When the fuse 206 is not blown, the pad 202 goes to the “L” level,turning off the CMOS transfer gate 200. At this time, an output from theinverter 203 goes to the “H” level. The N-channel MOS transistor 204turns on. The output node for the CMOS transfer gate 200 is set to theground voltage.

The circuit in FIG. 22 can selectively control chip address output byblowing or not blowing the fuse 206.

During the chip initialization, it is also effective to configure thePMOS transistor so that the transistor turns on for the chip with chipAdd0 and turns off for a specific or all chips with chip Add1 or higher.

When the package includes only one chip as shown in FIG. 18, the chipaddress is set to 0. When a chip with chip address 1 is configured toalways turn on the PMOS transistor 58, a product including a single chipautomatically turns off the PMOS transistor. A chip including aplurality of chips necessarily includes two chips with chip addresses 0and 1. Such product turns on the PMOS transistor in the chip with chipaddress 1. The above-mentioned pull-up operation is implementedautomatically. Thus, it is easy to configure a chip with chip address 1to always perform a pull-up operation during the chip initialization byusing the circuits in FIGS. 20 through 22 and configuring boding andfuse setting. Further, it is possible to configure a chip with chipaddress 1 to always perform a pull-up operation during the chipinitialization by providing all chips with the circuit in FIGS. 23A and23B having chip Add0 changed to chip Add1 for the circuit in FIGS. 19Aand 19B. In this case, there is no need the configuring boding and fusesetting.

FIG. 24 shows a memory device according to a seventh embodiment of thepresent invention by using the above-mentioned method (B) when the useror the system does not monitor the wire 17 for busy state output. FIG.24 is a circuit diagram specifically showing a partial configuration ofthe busy control circuit 32 in FIG. 4 provided for each of the twomemory chips MC1 and MC2 in FIG. 3.

The busy control circuit 32 has the same circuit configuration in bothmemory chips MC1 and MC2. The busy control circuits are represented bythe reference numerals 32-1 and 32-2 in the memory chips MC1 and MC2,respectively. The busy control circuits 32-1 and 32-2 in the memorydevice according to the seventh embodiment have basically the sameconfiguration as that shown in FIG. 17. The mutually corresponding partsin FIGS. 24 and 17 are designated by the same reference numerals and adetailed description is omitted for simplicity. The following describesonly portions that differ from FIG. 17.

The memory device in FIG. 17 connects the P-channel MOS transistor 58between the load resistor 57 and the node for the power supply voltageVcc. Instead, the seventh embodiment connects an N-channel MOStransistor 59 therebetween. Accordingly, the gate of the N-channel MOStransistor 59 is supplied with logically inverted control signals /P1and /P2 instead of P1 and P2.

It is to be distinctly understood that the present invention is notlimited to the above-mentioned embodiments but may be otherwisevariously embodied within the spirit and scope of the invention.According to the above-mentioned embodiments, the memory cell comprisesthe NAND-cell type EEROM. Each NAND cell is provided with eight seriallyconnected memory cells. Obviously, the present invention can be embodiedwhen each NAND cell may contain one, two, four, 16, 32, or 64 memorycells.

In addition to the memory chip including the NAND-cell type EEROM, forexample, it may be preferable to use a memory chip including theNOR-cell type EEROM according to the equivalent circuit in FIG. 25, amemory chip including the DINOR-cell type EEROM according to theequivalent circuit in FIG. 26, a memory chip including the AND-cell typeEEROM according to the equivalent circuit in FIG. 27, and a memory chipincluding the NOR-cell type EEROM with the selective transistoraccording to the equivalent circuit in FIG. 28. The details of theDINOR-cell type EEROM are described in H. Onoda et al., IEDM TechnicalDigest Paper, 1992. pp. 599-602. The details of the AND-cell type EEROMare described in H. Kume et al., IEDM Technical Digest Paper, 1992. pp.991-993.

The above-mentioned embodiments have been described by using thenonvolatile semiconductor memory device capable of electricallyrewriting data as an example. The present invention can be likewiseembodied for the other semiconductor memory devices.

Further, the above-mentioned embodiments have explained that the nodefor the busy signal /BusyA is pulled up only during the initializationoperation at the power-on time in the memory chip. The node for the busysignal /BusyA can be pulled up otherwise, e.g., during a normaloperation period or when only one memory chip is provided. In this case,in the system which monitors the busy signal /Busy A, there is providedan effect of not having to provide a pull-up circuit outside thepackage.

The above-mentioned embodiments have explained the case where a pull-upoperation is performed irrespectively of whether the memory chipselected for the pull-up operation is busy or ready. It is possible tocontrol not to perform a pull-up operation when the memory chip selectedfor the pull-up operation is busy, for example. When the selected memorychip is busy, the transistor 56 in the busy control circuit 32-1 in FIG.17 stays the on state. In this state, turning on the transistor 58generates a current between the power supply voltage Vcc and the groundvoltage GND, just increasing a wasteful current. It is desirable to pullup the node for the busy signal /BusyA only when the memory chipselected for the pull-up operation is ready, only during theinitialization at the power-on time, or during a normal operation. As aresult, it is possible to offer low power consumption. The presentinvention is also effective when the circuits embodied in FIGS. 23A and23B are modified to those shown in FIGS. 34A and 34B, 35A and 35B, 36,37A and 37B.

The present invention is also effective when the circuits embodied inFIGS. 13 through 17 are modified to those shown in FIGS. 29 through 33.The modified circuits in FIGS. 29 through 33 show configuration examplesin which the serially connected two inverters 60 replace the ANDcircuits 54 and 55 in the embodied circuits in FIGS. 13 through 17.

The modified circuits in FIGS. 29 through 33 also can provide operationsequivalent to those for the embodied circuits in FIGS. 13 through 17.The use of two inverters can decrease the number of elements.

Obviously the present invention is effective when the busy state outputpad generates an inverted signal level polarity.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A semiconductor memory system comprising: a plurality of firstnonvolatile memory chips, wherein an initialization operation isperformed in each of the plurality of first nonvolatile memory chipsafter a power-on sequence, a first busy state is maintained as long asthe initialization operation is performed in at least one of theplurality of first nonvolatile memory chips, the first busy state ismaintained until the initialization operation is completed in all of theplurality of first nonvolatile memory chips, the first busy state isreleased after the initialization operation is completed in all of theplurality of first nonvolatile memory chips.
 2. The semiconductor memorysystem according to claim 1, further comprising: a plurality of I/Opads, each of the plurality of first nonvolatile memory chips comprisingthe plurality of I/O pads, wherein the plurality of I/O pads of one ofthe plurality of first nonvolatile memory chips are respectivelyconnected to corresponding I/O pads of another of the plurality of firstnonvolatile memory chips.
 3. The semiconductor memory system accordingto claim 1, further comprising: a busy state output pad, each of theplurality of first nonvolatile memory chips comprising the busy stateoutput pad, wherein the busy state output pad of one of the plurality offirst nonvolatile memory chips is connected to the busy state output padof another of the plurality of first nonvolatile memory chips.
 4. Thesemiconductor memory system according to claim 3, further comprising: abusy state output pad detection circuit, each of the plurality of firstnonvolatile memory chips comprising the busy state output pad detectioncircuit, wherein the busy state output pad detection circuit detects avoltage level of the busy state output pad.
 5. The semiconductor memorysystem according to claim 3, wherein the busy state output pad is set toa first voltage as long as the initialization operation is performed inat least one of the plurality of first nonvolatile memory chips, and thebusy state output pad is set to a second voltage after theinitialization operation is completed in all of the plurality of firstnonvolatile memory chips, the first voltage is different from the secondvoltage.
 6. The semiconductor memory system according to claim 5,wherein the first voltage is lower than the second voltage.
 7. Thesemiconductor memory system according to claim 5, further comprising: abusy state output pad detection circuit, each of the plurality of firstnonvolatile memory chips comprising the busy state output pad detectioncircuit, wherein the busy state output pad detection circuit detects avoltage level of the busy state output pad.
 8. The semiconductor memorysystem according to claim 7, further comprising: a plurality of I/Opads, each of the plurality of first nonvolatile memory chips comprisingthe plurality of I/O pads, wherein the plurality of I/O pads of one ofthe plurality of first nonvolatile memory chips are respectivelyconnected to corresponding I/O pads of another of the plurality of firstnonvolatile memory chips, at least one of the plurality of I/O padsoutputs a busy signal in response to an input command, the busy signalis set to a third voltage corresponding to the first busy state as longas the busy state output pad is set to the first voltage, the busysignal is set to a fourth voltage corresponding to a second busy stateas long as the busy state output pad is set to the second voltage, thefirst busy state is different from the second busy state, the thirdvoltage is different from the fourth voltage.
 9. The semiconductormemory system according to claim 1, wherein each of the plurality offirst nonvolatile memory chips is an EEPROM chip.
 10. The semiconductormemory system according to claim 1, wherein each of the plurality offirst nonvolatile memory chips has a memory cell array in which memorycell units are arranged in a matrix, the memory cell units eachincluding a plurality of nonvolatile memory cells connected in seriesand a select gate transistor.
 11. A semiconductor memory systemcomprising: a package; and a plurality of first nonvolatile memory chipsincluded in the package; wherein an initialization operation isperformed in each of the plurality of first nonvolatile memory chipsafter a power-on sequence, a first busy state is maintained as long asthe initialization operation is performed in at least one of theplurality of first nonvolatile memory chips, the first busy state ismaintained until the initialization operation is completed in all of theplurality of first nonvolatile memory chips, the first busy state isreleased after the initialization operation is completed in all of theplurality of first nonvolatile memory chips.
 12. The semiconductormemory system according to claim 11, further comprising: a plurality ofI/O pads, each of the plurality of first nonvolatile memory chipscomprising the plurality of I/O pads, wherein the plurality of I/O padsof one of the plurality of first nonvolatile memory chips arerespectively connected to corresponding I/O pads of another of theplurality of first nonvolatile memory chips in the package.
 13. Thesemiconductor memory system according to claim 11, further comprising: abusy state output pad, each of the plurality of first nonvolatile memorychips comprising the busy state output pad, wherein the busy stateoutput pad of one of the plurality of first nonvolatile memory chips isconnected to the busy state output pad of another of the plurality offirst nonvolatile memory chips in the package.
 14. The semiconductormemory system according to claim 13, further comprising: a busy stateoutput pad detection circuit, each of the plurality of first nonvolatilememory chips comprising the busy state output pad detection circuit,wherein the busy state output pad detection circuit detects a voltagelevel of the busy state output pad.
 15. The semiconductor memory systemaccording to claim 13, wherein the busy state output pad is set to afirst voltage as long as the initialization operation is performed in atleast one of the plurality of first nonvolatile memory chips, and thebusy state output pad is set to a second voltage after theinitialization operation is completed in all of the plurality of firstnonvolatile memory chips, the first voltage is different from the secondvoltage.
 16. The semiconductor memory system according to claim 15,wherein the first voltage is lower than the second voltage.
 17. Thesemiconductor memory system according to claim 15, further comprising: abusy state output pad detection circuit, each of the plurality of firstnonvolatile memory chips comprising the busy state output pad detectioncircuit, wherein the busy state output pad detection circuit detects avoltage level of the busy state output pad.
 18. The semiconductor memorysystem according to claim 17, further comprising: a plurality of I/Opads, each of the plurality of first nonvolatile memory chips comprisingthe plurality of I/O pads, wherein the plurality of I/O pads of one ofthe plurality of first nonvolatile memory chips are respectivelyconnected to corresponding I/O pads of another of the plurality of firstnonvolatile memory chips, at least one of the plurality of I/O padsoutputs a busy signal in response to an input command, the busy signalis set to a third voltage corresponding to the first busy state as longas the busy state output pad is set to the first voltage, the busysignal is set to a fourth voltage corresponding to a second busy stateas long as the busy state output pad is set to the second voltage, thefirst busy state is different from the second busy state, the thirdvoltage is different from the fourth voltage.
 19. The semiconductormemory system according to claim 11, wherein each of the plurality offirst nonvolatile memory chips is an EEPROM chip.
 20. The semiconductormemory system according to claim 11, wherein each of the plurality offirst nonvolatile memory chips has a memory cell array in which memorycell units are arranged in a matrix, the memory cell units eachincluding a plurality of nonvolatile memory cells connected in seriesand a select gate transistor.
 21. A semiconductor memory systemcomprising: a plurality of first nonvolatile memory chips eachcomprising a plurality of I/O pads, wherein an initialization operationis performed in each of the plurality of first nonvolatile memory chipsafter a power-on sequence, a first busy state is maintained as long asthe initialization operation is performed in at least one of theplurality of first nonvolatile memory chips, the first busy state ismaintained until the initialization operation is completed in all of theplurality of first nonvolatile memory chips, the first busy state isreleased after the initialization operation is completed in all of theplurality of first nonvolatile memory chips, the plurality of I/O padsof one of the plurality of first nonvolatile memory chips arerespectively connected to corresponding I/O pads of another of theplurality of first nonvolatile memory chips, at least one of theplurality of I/O pads outputs a busy signal in response to an inputcommand, the busy signal is set to a first voltage corresponding to thefirst busy state as long as the initialization operation is performed inat least one of the plurality of first nonvolatile memory chips, thebusy signal is set to a second voltage corresponding to a second busystate after the initialization operation is completed in all of theplurality of first nonvolatile memory chips, the first busy state isdifferent from the second busy state, the first voltage is differentfrom the second voltage.
 22. The semiconductor memory system accordingto claim 21, further comprising: a busy state output pad, each of theplurality of first nonvolatile memory chips comprising the busy stateoutput pad, wherein the busy state output pad of one of the plurality offirst nonvolatile memory chips is connected to the busy state output padof another of the plurality of first nonvolatile memory chips.
 23. Thesemiconductor memory system according to claim 22, wherein the busystate output pad is set to a third voltage as long as the initializationoperation is performed in at least one of the plurality of firstnonvolatile memory chips, and the busy state output pad is set to afourth voltage after the initialization operation is completed in all ofthe plurality of first nonvolatile memory chips, the third voltage isdifferent from the fourth voltage.
 24. The semiconductor memory systemaccording to claim 21, wherein each of the plurality of firstnonvolatile memory chips is an EEPROM chip.
 25. The semiconductor memorysystem according to claim 21, wherein each of the plurality of firstnonvolatile memory chips has a memory cell array in which memory cellunits are arranged in a matrix, the memory cell units each including aplurality of nonvolatile memory cells connected in series and a selectgate transistor.
 26. A semiconductor memory system comprising: apackage; and a plurality of first nonvolatile memory chips eachcomprising a plurality of I/O pads, the plurality of first nonvolatilememory chips being included in the package, wherein an initializationoperation is performed in each of the plurality of first nonvolatilememory chips after a power-on sequence, a first busy state is maintainedas long as the initialization operation is performed in at least one ofthe plurality of first nonvolatile memory chips, the first busy state ismaintained until the initialization operation is completed in all of theplurality of first nonvolatile memory chips, the first busy state isreleased after the initialization operation is completed in all of theplurality of first nonvolatile memory chips, the plurality of I/O padsof one of the plurality of first nonvolatile memory chips arerespectively connected to corresponding I/O pads of another of theplurality of first nonvolatile memory chips, at least one of theplurality of I/O pads outputs a busy signal in response to an inputcommand, the busy signal is set to a first voltage corresponding to thefirst busy state as long as the initialization operation is performed inat least one of the plurality of first nonvolatile memory chips, thebusy signal is set to a second voltage corresponding to a second busystate after the initialization operation is completed in all of theplurality of first nonvolatile memory chips, the first busy state isdifferent from the second busy state, the first voltage is differentfrom the second voltage.
 27. The semiconductor memory system accordingto claim 26, further comprising: a busy state output pad, each of theplurality of first nonvolatile memory chips comprising the busy stateoutput pad, wherein the busy state output pad of one of the plurality offirst nonvolatile memory chips is connected to the busy state output padof another of the plurality of first nonvolatile memory chips in thepackage.
 28. The semiconductor memory system according to claim 27,wherein the busy state output pad is set to a third voltage as long asthe initialization operation is performed in at least one of theplurality of first nonvolatile memory chips, and the busy state outputpad is set to a fourth voltage after the initialization operation iscompleted in all of the plurality of first nonvolatile memory chips, thethird voltage is different from the fourth voltage.
 29. Thesemiconductor memory system according to claim 26, wherein each of theplurality of first nonvolatile memory chips is an EEPROM chip.
 30. Thesemiconductor memory system according to claim 26, wherein each of theplurality of first nonvolatile memory chips has a memory cell array inwhich memory cell units are arranged in a matrix, the memory cell unitseach including a plurality of nonvolatile memory cells connected inseries and a select gate transistor.